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【判断题】
(2)(是非题)我国正在下大力气优先发展教育,办人民满意的教育。( )A.
正确
B.
错误
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【单选题】Although spliceosomal introns seem to be limited to eukaryotes, the other three intron classes are not. Genes with group I and II introns have now been found in both bacteria and bacterial viruses. Ba...
A.
group I
B.
group I I
C.
group I II
D.
group IV
【简答题】组成箭头所指结构
【多选题】How does RNA catalyze the splicing of introns in eukaryotic cells?
A.
There are four classes of introns. The first two, the group I and group II introns, differ in the details of their splicing mechanisms but share one surprising characteristic: they are self-splicing—no protein enzymes are involved.
B.
Group I introns are found in some nuclear, mitochondrial, and chloroplast genes that code for rRNAs, mRNAs, and tRNAs. Group II introns are generally found in the primary transcripts of mitochondrial or chloroplast mRNAs in fungi, algae, and plants. Group I and group II introns are also found among the rare examples of introns in bacteria.
C.
Neither class requires a high-energy cofactor (such as ATP) for splicing. The splicing mechanisms in both groups involve two transesterification reaction steps, in which a ribose 2′- or 3′-hydroxyl group makes a nucleophilic attack on a phosphorus, and a new phosphodiester bond is formed at the expense of the old, maintaining the balance of energy.
D.
These reactions are very similar to the DNA breaking and rejoining reactions promoted by topoisomerases and site-specific recombinases.
【简答题】组成箭头所指结构
【单选题】As many as ______ of miRNA genes may lie in the introns or even exons of other genes. These are usually, though not exclusively, found in a sense orientation, and thus usually are regulated together w...
A.
20%
B.
30%
C.
40%
D.
50%
【简答题】组成箭头所指结构
【简答题】已知椭圆 上的一点 到椭圆一个焦点的距离为 ，则 到另一焦点距离为
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